The present invention relates generally to aluminum alloys and more specifically to L12 phase dispersion strengthened aluminum alloys having ceramic reinforcement particles. The combination of high strength, ductility, and fracture toughness, as well as low density, make aluminum alloys natural candidates for aerospace and space applications. However, their use is typically limited to temperatures below about 300° F. (149° C.) since most aluminum alloys start to lose strength in that temperature range as a result of coarsening of strengthening precipitates.
The development of aluminum alloys with improved elevated temperature mechanical properties is a continuing process. Some attempts have included aluminum-iron and aluminum-chromium based alloys such as Al—Fe—Ce, Al—Fe—V—Si, Al—Fe—Ce—W, and Al—Cr—Zr—Mn that contain incoherent dispersoids. These alloys, however, also lose strength at elevated temperatures due to particle coarsening. In addition, these alloys exhibit ductility and fracture toughness values lower than other commercially available aluminum alloys.
Other attempts have included the development of mechanically alloyed Al—Mg and Al—Ti alloys containing ceramic dispersoids. These alloys exhibit improved high temperature strength due to the particle dispersion, but the ductility and fracture toughness are not improved.
U.S. Pat. No. 6,248,453 discloses aluminum alloys strengthened by dispersed Al3X L12 intermetallic phases where X is selected from the group consisting of Sc, Er, Lu, Yb, Tm, and U. The Al3X particles are coherent with the aluminum alloy matrix and are resistant to coarsening at elevated temperatures. The improved mechanical properties of the disclosed dispersion strengthened L12 aluminum alloys are stable up to 572° F. (300° C.). In order to create aluminum alloys containing fine dispersions of Al3X L12 particles, the alloys need to be manufactured by expensive rapid solidification processes with cooling rates in excess of 1.8×103 F/sec (103° C./sec). U.S. Patent Application Publication No. 2006/0269437 A1 discloses an aluminum alloy that contains scandium and other elements. While the alloy is effective at high temperatures, it is not capable of being heat treated using a conventional age hardening mechanism.
It is desirable for aluminum alloys with L12 precipitates to have balanced mechanical properties suitable for high performance applications. Scandium forms an Al3Sc precipitate in aluminum alloys that is strong and thermally stable. The addition of gadolinium and zirconium improves thermal stability of the alloy by substitution of gadolinium and zirconium into the Al3Sc precipitate. This alloy has high strength for a wide temperature range of −423° F. (−253° C.) up to about 600° F. (316° C.). It would be desirable to increase the strength and modulus of dispersion strengthened L12 aluminum alloys at room temperature and elevated temperatures by increasing resistance to dislocation movement and by transferring load to stiffer reinforcements.